Fungi case challenge 1
A housewife presents with the lesion shown (fig 1a), which has been present for three weeks. One of her children has several similar lesions on the neck and chest.
Which terms best describe the lesion?
#! Erythema || Red skin due to increased blood supply. Blanches with pressure.
#! Scaling || Flaking skin due to an increase in the dead cells on the surface of the skin (stratum corneum).
#! Plaque || A palpable flat lesion greater than 0.5 cm diameter. Most plaques are elevated, but a plaque can also be a thickened area without being visibly raised above the skin surface. They may have well-defined or ill-defined borders.
What is the most appropriate diagnosis?
*! Tinea faciei
Explanation: The image shows an erythematous scaly plaque, characteristic of an inflammatory dermatophyte infection (known as tinea faciei when it affects the face).
Explanation: Impetigo presents as a crusted or blistered erythematous plaque and is sometimes difficult to distinguish from a tinea infection. Folliculitis presents as follicular pustules -sometimes seen within the scaly plaque due to fungal infection. Abscesses are nodules greater than 1cm in diameter full of pus and may be seen in very inflammatory tinea (kerion).
What is the likely organism(s)?
# _Trichophyton rubrum_
#! _Microsporum canis_
# _Candida albicans_
# _Scopulariopsis brevicaulis_
Explanation: Inflammatory tinea infections are most often caused by a zoophilic species. The family had recently obtained a kitten and the responsible organism was Microsporum canis.
Explanation: T. rubrum is the cause of tinea pedis and other non-inflammatory tinea infections. C. albicans favours mucosal and flexural surfaces. S. brevicaulis is a mould that occasionally causes chronic toenail infections.
What is the best way to confirm the infection is due to M. canis?
* Smear for wet ground examination
* Blue-top swab for microscopy and culture
*! Scraping for microscopy and culture
* Wood’s light examination
Explanation: Gently scrape the scale from the surface of the lesion and transport in a sterile container or black envelope for microscopy and culture. The microbiology laboratory will treat the skin scrapings with potassium hydroxide solution, stain and report the microscopy findings within a few days. The results of fungal culture will usually be reported in 4 weeks.
Explanation: Although Wood's light examination can be used to detect M. canis infection because the organism results in green fluorescence, it is frequently negative in lesions on glabrous (non-hairy) skin as the inflammatory responses means there are very few organisms.
Explanation: Wet ground examinations are useful for spirochaetes; swabs are used for bacterial microscopy and culture.
The lesion was treated with a topical antifungal medication. Which one would you select?
* Povidone iodine
Explanation: The correct response is clotrimazole; imidazole creams are effective against dermatophytes.
Explanation: Nystatin is only effective against yeasts and is not useful for dermatophyte infections. Povidone iodine has some effect against fungi but is not likely to clear the infection. Griseofulvin is an orally active antifungal agent and is not available in a topical preparation.